Solid-State <sup>17</sup>O NMR of Unstable Acyl-Enzyme Intermediates: A Direct Probe of Hydrogen Bonding Interactions in the Oxyanion Hole of Serine Proteases
Bibliographic record
Abstract
We report preparation, trapping, and solid-state 17 O NMR characterization of three unstable acyl-enzyme intermediates (≈ 26 kDa): p - N, N -dimethylamino-[ 17 O]benzoyl-chymotrypsin, trans - o -methoxy-[ 17 O]cinnamoyl-chymotrypsin, and trans - p -methoxy-[ 17 O]cinnamoyl-chymotrypsin. We show that both the 17 O chemical shifts and nuclear quadrupolar parameters obtained for these acyl-enzyme intermediates in the solid state are correlated with their deacylation rate constants measured in aqueous solution. With the aid of quantum mechanical calculations, the experimental 17 O NMR parameters were interpreted as to reflect the hydrogen bonding interactions between the carbonyl (C═ 17 O) functional group of the acyl moiety and the two NH groups from the protein backbone (Ser195 and Gly193) in the oxyanion hole, a general feature of all serine proteases. Our results further suggest that the 17 O chemical shift and quadrupole coupling constant display distinctly different sensitivities toward different aspects of hydrogen bonding, such as hydrogen bond distance and direction. This work demonstrates the utility of 17 O as a useful nuclear probe in NMR studies of enzymes.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".